Micro-encapsulation is used in a large variety of different applications where a compound needs to be delivered or applied to a target area while prior to delivery the compound needs to be protected from its environment, or where that compound needs to be released in a time-delayed way or only after a treatment has been applied that triggers release. Various techniques for preparing microcapsules are known in the art and are used, depending on the contents to be encapsulated, the environment wherein the microcapsules should retain their integrity and the desired release mechanism.
Interfacial polycondensation is a well-known technique for preparing microcapsules and versatile microcapsule wall materials that can be produced are polyureas and polyurethanes. Such wall materials are produced by having a first phase which is water-immiscible and comprises a polyfunctional isocyanate, i.e. a diisocyanate and/or a polyisocyanate, and a second aqueous phase which may comprise a polyfunctional alcohol or amine, i.e. a diol and/or polyol for obtaining a polyurethane capsule wall or a diamine and/or polyamine comprising —NH2 and/or —NH groups for obtaining a polyurea capsule wall.
If the material to be encapsulated is hydrophobic it will be included in the water-immiscible phase, whereafter the two phases are mixed by high shear mixing to form an oil-in-water emulsion. In this emulsion the polycondensation reaction will take place. Thus, the small droplets of the water-immiscible phase will be surrounded by the microcapsule wall formed by polycondensation of the isocyanate and the polyalcohol or polyamine as starting materials. Conversely, if the material to be encapsulated is hydrophilic, it will be included in the aqueous phase and the mixture of the two phases converted into a water-in-oil emulsion. The polycondensation reaction will then form microcapsule walls surrounding the droplets of water-miscible phase. Suitable emulsifiers are often utilized to aid in the preparation of, and to stabilise, the emulsion.
Suitable raw materials and processes for preparing microcapsules by polycondensation are described in U.S. Pat. No. 4,640,709 and the literature described therein. As is exemplified therein, and also in U.S. Pat. No. 6,133,197, polyurea and polyurethane microcapsules are often used for rugged applications, such as for encapsulation of agrochemicals e.g. herbicides and pesticides, where slow time-release is desired to set the agents free. For such applications the microcapsules also require a relatively high mechanical strength. For the polycondensation reaction a wide variety of suitable diisocyanate and symmetrical triisocyanate starting materials is disclosed in the prior art.
For the release of benefit agents intended for laundry, washing, cleaning, surface care and personal and skin care no polyurea or polyurethane microcapsules have thus far been applied. For such applications quicker and easier release and/or less mechanical strength are often desirable. Also it would be desirable to more precisely influence the capsule wall permeability and other capsule wall properties to achieve the desired release profile and consumer benefits